1. Field of the Invention
Embodiments of the present invention relate to a display device, and more particularly, an organic electroluminescent device and a method of manufacturing the same.
2. Discussion of the Related Art
A representative example of a flat panel display is a Liquid Crystal Display (LCD) device that is light in weight and consumes a small amount of power. Thus, the LCD device has been widely used as the flat panel display throughout the world. However, the LCD device is not a light emitting device. That is, it is necessary for the LCD device to use an additional light source, for example, a backlight unit to emit the light. Also, the LCD device has technical limitations in brightness, contrast, and viewing angle, and has difficulty in increasing the size of a valid display area. To solve the above-mentioned problems, many developers are conducting intensive research into an improved flat panel display.
An organic electroluminescent device is a self-light-emitting device. The organic electroluminescent device has a desirable viewing angle and contrast, which are superior to those of the LCD device. There is no need to use a backlight. The organic electroluminescent device can be made small in size, light in weight, and thin in thickness. Also, the organic electroluminescent device has power consumption superior to that of the LCD device. For example, the organic electroluminescent device can be driven at a DC low voltage, has rapid response speed, has very strong resistance to an external impact because it is made of solids, has a wide range of available temperature, and is composed of a low-priced components. As a result, the organic electroluminescent device is superior to the liquid crystal display (LCD) device.
A fabrication process of the organic electroluminescent device is mostly composed of a deposition process and an encapsulation process, different from the liquid crystal display (LCD) and a Plasma Display Panel (PDP), such that the fabrication process of the organic electroluminescent device is considered to be very simple.
FIG. 1 is a schematic diagram illustrating bands of a unit pixel of a related art organic electroluminescent device. Referring to FIG. 1, the organic electroluminescent device includes a hole transport layer 3 (also called a hole transport layer), a light emitting layer 4 (also called a light emitting layer), and an electron transport layer 5 (also called an electron transport layer), which are located between an anode electrode 1 and a cathode electrode 7. To effectively inject holes and electrons, the organic electroluminescent device may further include a hole injection layer 2 and an electron injection layer 6, which are located between the electron transport layer 5 and the cathode electrode 7. In this case, holes are transmitted from the anode electrode 1 to the hole injection layer 2 and the hole transport layer 3, and are then injected into the light emitting layer 4. Electrons are transmitted from the cathode electrode 7 to the electron injection layer 6 and the electron transport layer 5, and are then injected into the light emitting layer 4. The holes and the electrons form an excitation 8, such that the excitation 8 generates the light corresponding to energy between the electron and the hole.
The anode electrode 1 is selected from a transparent conductive material having a high work function, such as an ITO (Indium Tin Oxide), an IZO (Indium Zinc Oxide), and an ITZO (Indium Tin Zinc Oxide)), such that the light passed through the anode electrode 1. The cathode electrode 7 is selected from a chemically stable metal having a low work function.
The above-mentioned organic electroluminescent device can form a light emitting layer having one of three colors (Red, Green, and Blue) for each pixel. The light emitting layer is mainly composed of a light emitting material.
During the fabrication process of the above-mentioned light emitting material, an irregular pattern occurs in the light emitting layer because light emitting materials of individual color areas have different dry times and different viscosities such that the light emitting layer is inappropriate for a fine light emitting layer of several micrometers and an unexpected mixed color occurs in the vicinity of an edge part of the light emitting layer, resulting in the deterioration of color purity.